President Barack Obama said the full resources of the federal government are being mobilized to investigate the deadly explosions today in Boston and he vowed those responsible will brought to justice.
"We still do not know who did this or why, and people shouldn't jump to conclusions before we have all the facts," Obama said at the White House. "Any responsible individuals, any responsible groups will feel the full weight of justice."
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He said security will be increased across the country "as necessary."
While Obama didn't use the word terrorism to describe the attack, an administration official, who wasn't authorized to speak publicly, said the bombings are being investigated as an act of terror.
The president was notified of the incident today about 3 p.m., 10 minutes after the twin blasts that killed two people and injured scores of others near the finish line of the Boston Marathon.
He was briefed on the investigation by FBI Director Robert Mueller and Homeland Security Secretary Janet Napolitano, according to a White House statement.
Obama also called Boston Mayor Tom Menino and Massachusetts Governor Deval Patrick and he directed federal agencies to help local authorities in the investigation.
"We don't yet have all the answers," Obama said. "As we get more information, our team will provide more briefings."
Senator Dianne Feinstein, the head of the Intelligence Committee, said there were no warnings.
"There is no intelligence to the best of my knowledge that would point out there was an attack on the way," Feinstein told reporters. There weren't "any hallmarks" to the attack "other than the fact it could be homegrown."
She said her committee has been in touch with U.S. intelligence agencies since the bombing, and what while she considers it a terrorist strike, she couldn't say if it was foreign or domestic.
Feinstein, a California Democrat, said the Boston Marathon was a "diabolical" place to strike.
"We've known for sometime that a public event where there were a lot of people would be subject to this possibility," she said.
Vice President Joe Biden was in the middle of a conference call on gun violence when he learned of the incident.
"As I'm speaking here they just turned on the TV in my office," Biden said. "I don't know any of the details of what caused it, who did it, but our prayers are with the people in Boston who have suffered injury."
Outside the White House, police restricted pedestrian traffic on the sidewalk and street immediately along the fence surrounding the executive mansion. The street was closed to vehicles following the 1995 bombing of a federal building in Oklahoma City. Tourists continued to stroll through Lafayette Park directly across Pennsylvania Avenue from the White House.
"Out of an abundance of caution, we have expanded our security perimeter at the White House complex," said Edwin Donovan, deputy assistant director at the Secret Service.